Returns a jar that'll automatically encrypt cookie values before
sending them to the client and will decrypt them for read. If the cookie
was tampered with by the user (or a 3rd party), nil will be
returned.

If config.action_dispatch.encrypted_cookie_salt and
config.action_dispatch.encrypted_signed_cookie_salt are both
set, legacy cookies encrypted with HMAC AES-256-CBC will be transparently
upgraded.

This jar requires that you set a suitable secret for the verification on
your app's secret_key_base.

Returns a jar that'll automatically generate a signed representation of
cookie value and verify it when reading from the cookie again. This is
useful for creating cookies with values that the user is not supposed to
change. If a signed cookie was tampered with by the user (or a 3rd party),
nil will be returned.

This jar requires that you set a suitable secret for the verification on
your app's secret_key_base.